I've heard of people opening up the servo and reversing leads on the drive motor and the sensing pot. I'm sure you could do a search and find some instructions.

Oh hell, here's a couple of links that describes how to do it. Took me 10 seconds to "google" it.

http://www.fatlion.com/sailplanes/servos.html
http://www.hitecrcd.com/Support/Faqs/Faq_Genservo_.htm (see "How can I reverse the direction of my analog servo?")